1. Field of the Invention
The present invention relates to transfer control apparatus used for optical image reading apparatus that reads images on paper such as characters and graphics while transferring the paper continuously, and more particularly, to transfer control apparatus of optical image reading apparatus selectively using a transmission-type sensor and a reflection-type sensor so as to detect paper.
2. Description of the Related Art
Presently, copy machines, facsimiles, image readers, and the like perform read processing by paper transfer, which use various paper sensors for detecting paper. As for such sensors for detecting paper, transmission-type sensors and reflection-type sensors are generally used. A transmission-type sensor is composed of a light emitting diode (LED) and a phototransistor (PT) that are placed opposite each other with a paper transfer surface being put between the LED and PT. The sensor detects a quantity of transmitted light that is decreased by the paper screening light when the paper passes between them. Therefore, if the quantity of transmitted light becomes smaller than a predetermined value, the sensor detects paper presence. On the other hand, a reflection-type sensor has similarly an LED and a PT, and detects the quantity of light reflected from the surface of the paper by crossing the detection region of the PT with the optical axis of the LED. Then, if the quantity of reflected light becomes bigger than a predetermined value, the sensor detects paper presence.
However, since environments using paper sensors are diversified, it is necessary to detect special paper such as paper with superimposed printing, matte printing, and the like; paper having different thickness such as thin paper like tracing paper, post cards, and business cards; and further, deformed paper like folded or wrinkled paper. In addition to above conditions, it is also necessary to advance improvement such as higher detection speed and cost reduction. Here, the transmission-type sensor can comparatively easily detect paper although there is difference of output conditions due to printed conditions, thickness, kinds, deformation, and the like. However, the transmission-type sensor having the body combined with an LED and a PT is limited in its application because of its one body structure. Furthermore, regarding a transmission-type sensor separately having an LED and a PT, adjustment of opposed positioning is complicated. Moreover, since optical axes of both elements face each other across a paper transfer path, paper powder easily attaches to the lower element. Therefore, it has a problem that the output of the sensor becomes low in use instead of no paper, and hence, difference between a detection level without paper and a detection level in presence of thin paper which has large quantity of transmitted light becomes small, thereby making a mistake of detection.
In addition, in the reflection-type sensor, the light emitted by an LED and reflected by the surface of paper enters into a PT, the quantity of this reflected light being affected by surface conditions of paper as well as printed color and thickness of the paper. Concretely, according as presence of gloss of the printed paper surface, an output of the reflection-type sensor greatly changes even if the paper surface seems to be dark for human eyes. Although most of ink and toner for printing have gloss in usual printing, the output of the reflection-type sensor becomes very small for the paper printed with matting ink and toner, thereby adjustment and correction of the sensor output level being necessary for detecting such paper.
Further, an optical image reading apparatus detects a front and back edges of paper with paper sensors, which are used as reference positions at the time of read processing. Therefore, it is desirable that paper detection can be always done at the constant positions regardless of color and kinds of paper. However, in case there is a black area of printing at sensor's detection positions like front and back edges of paper, the position of paper, where the sensor output passes the slice level for paper detection, is different from that in the case that there is a completely blank area in printing at sensor's detecting position. For example, if light emission current flowing into an LED is set so that a sensor output may coincide with the slice level when a white paper edge is just under the sensor, the sensor output does not arrive at the slice level in case of the black paper edge until the paper edge fully enters into a sensor emission area. Hence, since this detection delay becomes a position error, as it is, in case of the black paper edge, this makes timing control of read processing in the downstream of paper transfer cause the position error.
Furthermore, conventionally, dedicated forms have been used, and parameters regarding characteristics of paper transfer have been limited, the parameters including paper thickness, size, base color, printed color, a printing method, edge treatment like a tear-off, a binding hole, a friction coefficient by coating, a reflection factor, and adsorption by static electricity. However, recently, these parameter limitations have been abolished, and hence, the kinds of paper have been diversified. Consequently, depending on paper, occurrence of jamming and double-feed during transfer has become a problem. In particular, double-feed of paper may become a cause of the jamming. Moreover, in image reading requiring sequential processing such as forms and slips, if the double-feed can not be detected, the data on paper to be read is different from the electronic information on a computer. Hence, the reliability of an entire operational system is decreased. Then, in a conventional method for detecting the double-feed, if, based on the designated thickness in the prohibited ranges of printing and writing on the forms which were designated when their user designed the forms, for example, the output change of the transmission-type sensor exceeds the predetermined value, the event is decided to be the double-feed. However, in case the paper out of specified items is transferred, the double-feed can not be detected. In order to prevent such double-feed, the most secure way is the single slip input that an operator inputs one sheet of paper at a time. However, the input method requires heavy work load, and increase of operational cost and decrease of processing speed can not be avoided.